User equipment and method for packet based device-to-device (d2d) discovery in an lte network

ABSTRACT

Embodiments of a User Equipment (UE) and methods for packet based device-to-device (D2D) discovery in an LTE network are generally described herein. In some embodiments, UE may be enabled for proximity services and may be configured to receive signaling from an enhanced node B (eNB) indicating resources allocated for D2D discovery. The UE may configure a discovery packet in accordance with a predetermined configuration to have at least a discovery payload and a cyclic-redundancy check (CRC). The discovery payload may include discovery-related content. The UE may be configured to transmit the discovery packet on at least some of the indicated resources for receipt by a receiving UE. In some embodiments, a demodulation reference signal (DMRS) may be selected to indicate a payload size and/or MCS of the discovery packet&#39;s payload.

PRIORITY CLAIMS

This application is a continuation of U.S. patent application Ser. No.15/096,504, filed Apr. 12, 2016, which is a continuation of U.S. patentapplication Ser. No. 14/280,799, which claims the benefit of priorityunder 35 U.S.C. 119(e) to U.S. Provisional Patent Application Ser. No.61/863,902, filed Aug. 8, 2013, and to U.S. Provisional PatentApplication Ser. No. 61/909,938, filed Nov. 27, 2013, each of which isincorporated herein by reference in its entirety.

TECHNICAL FIELD

Embodiments pertain to wireless communications. Some embodiments relateto cellular networks such as 3GPP LTE (Long Term Evolution) networks.Some embodiments relate to direct device-to-device (D2D) communication.Some embodiments relate to D2D discovery in LTE networks. Someembodiments relate to user equipment (UE) enabled for proximity services(ProSe enabled UEs).

BACKGROUND

Support for direct D2D communication as an integrated part of a wirelesscommunication network is currently being considered for the furtherevolution of LTE networks. With direct D2D communication, user equipment(UE) may communicate directly with each other without involvement of abase station or an enhanced node B (eNB). One issue with D2Dcommunication is device discovery to enable D2D communications. Devicediscovery involves discovering one or more other discoverable UEs withincommunication range for D2D communication. Device discovery alsoinvolves being discovered by one or more other discovering UEs withincommunication range for D2D communications. There are many unresolvedissues with respect to device discovery for D2D communication includingthe signaling used for device discovery and the discovery informationconveyed during device discovery.

Thus there are general needs for UEs and methods for improved devicediscovery for D2D communication in LTE networks. There are also generalneeds for UEs and methods for signaling and conveying discoveryinformation for D2D discovery.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a portion of an end-to-end network architecture of an LTEnetwork in accordance with some embodiments;

FIG. 2 shows a structure for a resource grid including a discovery zonefor D2D communications in accordance with some embodiments;

FIG. 3A illustrates a discovery packet in accordance with someembodiments;

FIG. 3B illustrates a discovery packet in accordance with some alternateembodiments;

FIG. 4 illustrates D2D discovery packet processing in accordance withsome embodiments;

FIG. 5 illustrates a functional block diagram of a UE in accordance withsome embodiments; and

FIG. 6 is a procedure for packet-based D2D discovery in accordance withsome embodiments.

DETAILED DESCRIPTION

The following description and the drawings sufficiently illustratespecific embodiments to enable those skilled in the art to practicethem. Other embodiments may incorporate structural, logical, electrical,process, and other changes. Portions and features of some embodimentsmay be included in, or substituted for, those of other embodiments.Embodiments set forth in the claims encompass all available equivalentsof those claims.

FIG. 1 shows a portion of an end-to-end network architecture of an LTEnetwork with various network components in accordance with someembodiments. The network architecture comprises a radio access network(RAN) (e.g., as depicted, the E-UTRAN or evolved universal terrestrialradio access network) 100 and a core network 120 (e.g., shown as anevolved packet core (EPC)) coupled together through an S1 interface 115.For convenience and brevity sake, only a portion of the core network120, as well as the RAN 100, is shown.

The core network 120 includes mobility management entity (MME) 122,serving gateway (serving GW) 124 and packet data network gateway (PDNGW) 126. The RAN also includes enhanced node Bs (eNBs) 104 (which mayoperate as base stations) for communicating with user equipment (UE)102. The eNBs 104 may include macro eNBs and low power (LP) eNBs.

In accordance with some embodiments, the UEs 102 may be arranged fordevice-to-device (D2D) communications including D2D discovery of otherUEs for direct D2D communication. Some embodiments provide a physicallayer design for packet-based D2D discovery. In some embodiments, a UE,such as UE 112, may configure and transmit a discovery packet 101 (e.g.,rather than a discovery sequence) to realize D2D discovery. This allowsadditional discovery-related content to be shared directly between theUEs. In these embodiments, the UE 112 that transmits the discoverypacket 101 may be referred to as a discovering device since it isdiscovering another UE (e.g., UE 114). These embodiments are discussedin more detail below.

The MME is similar in function to the control plane of legacy ServingGPRS Support Nodes (SGSN). The MME manages mobility aspects in accesssuch as gateway selection and tracking area list management. The servingGW 124 terminates the interface toward the RAN 100 and routes datapackets between the RAN 100 and the core network 120. In addition, itmay be a local mobility anchor point for inter-eNB handovers and alsomay provide an anchor for inter-3GPP mobility. Other responsibilitiesmay include lawful intercept, charging, and some policy enforcement. Theserving GW 124 and the MME 122 may be implemented in one physical nodeor separate physical nodes. The PDN GW 126 terminates an SGi interfacetoward the packet data network (PDN). The PDN GW 126 routes data packetsbetween the EPC 120 and the external PDN and may be a key node forpolicy enforcement and charging data collection. It may also provide ananchor point for mobility with non-LTE accesses. The external PDN may beany kind of IP network as well as an IP Multimedia Subsystem (IMS)domain. The PDN GW 126 and the serving GW 124 may be implemented in onephysical node or separated physical nodes.

The eNBs 104 (macro and micro) terminate the air interface protocol andmay be the first point of contact for a UE 102. In some embodiments, aneNB 104 may fulfill various logical functions for the RAN 100 includingbut not limited to RNC (radio network controller functions) such asradio bearer management, uplink and downlink dynamic radio resourcemanagement and data packet scheduling, and mobility management.

The S1 interface 115 is the interface that separates the RAN 100 and theEPC 120. It is split into two parts: the S1-U, which carries trafficdata between the eNBs 104 and the serving GW 124, and the S1-MME, whichis a signaling interface between the eNBs 104 and the MME 122. The X2interface is the interface between eNBs 104. The X2 interface comprisestwo parts, the X2-C and X2-U. The X2-C is the control plane interfacebetween the eNBs 104, while the X2-U is the user plane interface betweenthe eNBs 104.

With cellular networks, LP cells are typically used to extend coverageto indoor areas where outdoor signals do not reach well or to addnetwork capacity in areas with very dense phone usage, such as trainstations. As used herein, the term LP eNB refers to any suitablerelatively lower power eNB for implementing a narrower cell (narrowerthan a macro cell) such as a femtocell, a picocell, or a micro cell.Femtocell eNBs are typically provided by a mobile network operator toits residential or enterprise customers. A femtocell is typically thesize of a residential gateway or smaller and generally connects to theuser's broadband line. Once plugged in, the femtocell connects to themobile operator's mobile network and provides extra coverage in a rangeof typically thirty to fifty meters for residential femtocells. Thus, aLP eNB might be a femtocell eNB since it is coupled through the PDN GW126. Similarly, a picocell is a wireless communication system typicallycovering a small area, such as in-building (offices, shopping malls,train stations, etc.) or more recently in-aircraft. A picocell eNB cangenerally connect through the X2 link to another eNB such as a macro eNBthrough its base station controller (BSC) functionality. A LP eNB may beimplemented with a picocell eNB since it may be coupled to a macro eNBvia an X2 interface. Picocell eNBs or other LP eNBs may incorporate someor all functionality of a macro eNB. In some cases, this may be referredto as an access point, base station or enterprise femtocell.

In some LTE embodiments, a physical downlink shared channel (PDSCH)carries user data and higher-layer signaling to a UE 102. The physicaldownlink control channel (PDCCH) carries information about the transportformat and resource allocations related to the PDSCH channel, amongother things. It also informs the UE 102 about the transport format,resource allocation, and H-ARQ information related to the uplink sharedchannel. Typically, downlink scheduling (assigning control and sharedchannel resource blocks to UEs within a cell) is performed at the eNB104 based on channel quality information fed back from the UEs 102 tothe eNB 104, and then the downlink resource assignment information maybe sent to a UE 102 on a physical downlink control channel (PDCCH) usedfor (and possibly assigned to) the UE 102.

The PDCCH uses CCEs (control channel elements) to convey the controlinformation. Before being mapped to resource elements, the PDCCHcomplex-valued symbols may be first organized into quadruplets, whichmay be permuted using a sub-block inter-leaver for rate matching. EachPDCCH is transmitted using one or more of CCEs, where each CCE maycorrespond to nine sets of four physical resource elements known asresource element groups (REGs). Four QPSK symbols are mapped to eachREG. The PDCCH may be transmitted using one or more CCEs, depending onthe size of DCI and the channel condition. There may be four or moredifferent PDCCH formats defined in LTE with different numbers of CCEs(e.g., aggregation level L=1, 2, 4, or 8).

FIG. 2 shows a structure for a resource grid including a discovery zonefor D2D communications in accordance with some embodiments. The depictedgrid is a time-frequency grid, called a resource grid, which is thephysical resource in the downlink or uplink in each slot. The smallesttime-frequency unit in a resource grid is denoted as a resource element(RE). The resource grid comprises a number of resource blocks (RBs)which describe the mapping of certain physical channels to resourceelements. Each resource block comprises a collection of resourceelements and in the frequency domain, represents the smallest quanta ofresources that may be allocated, although the scope of the embodimentsis not limited in this respect. There are several different physicalchannels that are conveyed using such resource blocks. The resource gridillustrated in FIG. 2 may comprise an LTE operation zone 202 which maycomprise a plurality of physical RBs (PRBs) for use by the RAN 100.

In accordance with some embodiments, a UE 112 (FIG. 1) may receivesignaling from an eNB 104 (FIG. 1) indicating a discovery zone 204within the LTE operation zone 202. The discovery zone 204 may comprise aplurality of PRBs 206 of a discovery resource. The UE 112 may transmit adiscovery packet 101 (FIG. 1) for receipt by one or more other UEs(e.g., UE 114 (FIG. 1)) for D2D discovery within some PRBs 206 of thediscovery zone 204. In some embodiments, the resources allocated for D2Ddiscovery may be resources of a physical-uplink shared channel (PUSCH),although the scope of the embodiments is not limited in this respect.

A PRB may be associated with a particular slot of a subframe in the timedimension and a particular group of frequency subcarriers in thefrequency dimension. Each PRB, for example, may be identified by a RBindex and a subframe index. In some embodiments, a discovery packet 101may be transmitted within M subframes of N resources blocks where M andN are at least one and may be greater than one. These embodiments aredescribed in more detail below.

In some embodiments, a PRB may comprise twelve sub-carriers in thefrequency domain by 0.5 ms (i.e., one slot) in the time domain. The PRBsmay be allocated in pairs (in the time domain), although this is not arequirement. In some embodiments, a PRB may comprise a plurality of REs.A RE may comprise one sub-carrier by one symbol. When a normal CP isused, a RB contains seven symbols. When an extended CP is used, the RBcontains six symbols. A delay spread that exceeds the normal CP lengthindicates the use of extended CP. Each subframe may be one millisecond(ms) and one frame may comprise ten such subframes.

There are two different approaches in D2D discovery: restricted/closedD2D discovery and open D2D discovery. Restricted/closed D2D discoverymay apply to use cases wherein a discoverable device may be discoveredonly by a select set of ProSe enabled discovering devices. A furtherimplication of closed device discovery is consideration of scenarioswherein a discovering device tries to discover particular ProSe enableddevice(s) (one or many from a set of ProSe enabled devices). Thus, forthis use case, a discovering device would be assumed to know the ProSeenabled device it wishes to discover in its proximity.

Contrary to closed D2D discovery, open device discovery considers usecases wherein a discoverable device may want itself to be discovered byall ProSe enabled devices in its proximity. From the perspective of thediscovering device, open device discovery implies that a discoveringdevice may not be assumed to be aware of the identity of other ProSeenabled devices prior to discovery. Consequently, the device discoverymechanism for open discovery should aim towards discovering as manyProSe enabled devices in its proximity as possible.

For open D2D discovery, an eNB 104 may have a limited control on thediscovery process among the UEs 102. In particular, an eNB 104 mayperiodically allocate certain discovery resources in the form of D2Ddiscovery zones 204 for a UE 102 to transmit discovery information. Asmentioned above, the discovery information may be in the form of adiscovery packet with payload information. The examples described beloware described with respect to a discovery packet with payloadinformation. The discovery related information that UEs 102 may intendto share with each other may include a unique ID for deviceidentification, a service identity, etc. (e.g., 48 bits or more) as thedata payload, which may be protected by a cyclic-redundancy check (CRC).The number of resource blocks for discovery packet transmission in openD2D discovery design, which is denoted as L_(RB) ^(D2D), may be one ormore, depending on the payload size and the overall discoveryperformance requirements.

In the examples illustrated below, the discovery zones may be periodicwith each discovery zone comprising some RBs in the frequency domain andseveral subframes in time domain. In FIG. 2 N_(RB) ^(D2D), n_(RB)^(start), N_(SF) ^(D2D) and n_(SF) ^(start) are denoted as the number ofallocated RBs, the starting RB index and the number of subframes, thestarting subframe index of each discovery zone, respectively. Theinformation regarding the partitioning of the D2D discovery zones (suchas discovery zone 204) may be semi-statically signaled by the eNB 104using radio-resource control (RRC) signaling or by system informationblocks (SIBs) for within network coverage scenarios. For a partialnetwork coverage scenario, such information may be forwarded by anin-network coordinator UE to a UE that may be outside network coverage.

In some embodiments, for open D2D discovery, a UE 102 configured for D2Dcommunication may randomly choose the subframe index and starting RBindex within the discovery zone 204 to transmit a discovery packet 101.In some embodiments, the UE 102 may be configured for either open D2Ddiscovery or closed D2D discovery. When configured for closed D2Ddiscovery, an initial subframe within the discovery zone 204 may beassigned by the eNB 102 for transmission of the discovery packet 101.When configured for open D2D discovery, an initial subframe with thediscovery zone 204 may be selected (e.g., randomly) by the UE 102 fortransmission of the discovery packet 101. In some embodiments whenconfigured for open D2D discovery the initial subframe with thediscovery zone 204 may be randomly selected by the UE 102 fortransmission of the discovery packet 101, although the scope of theembodiments is not limited in this respect.

For outside and partial network coverage scenarios, such information maybe forwarded by the coordinator UE to the UEs that are outside networkcoverage. In these embodiments, for UEs that are outside the networkcoverage region, the configuration details for the D2D discovery zonemay be either pre-configured or relayed by a UE within network coverage,or the configuration details may be configured by another UE outsidenetwork coverage. In some embodiments, a pool of resources constitutingthe discovery zone 204 may be associated with or configured by asynchronization source or any other coordinator UE. In theseembodiments, a UE 102 may either be in a partial network coveragescenario if, for example, there is a presence of a network close by andit can communicate with and/or discover other UEs that are withinnetwork coverage, or fully outside network coverage.

For partial network coverage scenarios, discovery resources may beconfigured by an eNB 104 and may be relayed by another UE (e.g., acoordinator UE) that is within network coverage (and so, withinoperation zone of the network). For outside network coverage case, aspecific spectrum may be allocated, although the scope of theembodiments is not limited in this respect. Once a UE determines that itis not under any network coverage or cannot detect synchronizationsignals that have originated from the network, the UE may search forsynchronization signals on certain pre-configured spectrum band(s) forsynchronization signals that may be transmitted by other UEs (i.e., notoriginating from an eNB 104), and for the latter case, the resources maybe associated with the originating source of the synchronization signalor may be pre-configured.

As illustrated in FIG. 2, a discovery zone 204 may include one or moredemodulation reference signal (DMRS) symbols 210. In some embodiments,resource elements 211 that are adjacent to DMRS symbols 210 may be usedfor D2D discovery. These embodiments are described in more detail below.

FIGS. 3A and 3B illustrate discovery packets in accordance with variousembodiments. Discovery packet 300 (FIG. 3A) and discovery packet 320(FIG. 3B) may be suitable for use as discovery packet 101 (FIG. 1).Discovery packet 300 includes a discovery payload 304 and acyclic-redundancy check (CRC) 306. Discovery packet 320 includes adiscovery header 322, a discovery payload 324 and a CRC 326. Discoverypacket 300 does not include a header.

In accordance with embodiments, a UE, such as UE 112 (FIG. 1) enabledfor proximity services (ProSe enabled) may be configured forpacket-based D2D discovery operations in an LTE network, such as network100 (FIG. 1). In these embodiments, the UE 112 may be configured toreceive signaling from an eNB 104 (FIG. 1) indicating resources of adiscovery zone 204 (FIG. 2) allocated for D2D discovery. A UE 112 mayconfigure a discovery packet (i.e., discovery packet 300 (FIG. 3A) ordiscovery packet 320 (FIG. 3B)) in accordance with a predeterminedconfiguration to have at least a discovery payload 304/324 and a CRC306/326. The discovery payload 304/324 may include discovery-relatedcontent. The UE 112 may also be configured to transmit the discoverypacket 101 on at least some of the indicated discovery resources (e.g.,PRBs 206 of discovery zone 204) for receipt by a receiving UE 114. Inthese embodiments, a discovery packet, rather than a discovery sequence,is used to realize D2D discovery. This allows additionaldiscovery-related content to be shared between UEs. In theseembodiments, the UE 112 that transmits the discovery packet 101 may bereferred to as a discovering device since it is discovering another UE(i.e., UE 114) and UE 114 may be referred to as a discoverable device.

In these embodiments, a discovery packet 300 may be configured without aheader while in other embodiments, a discovery packet 320 may beconfigured with a header 322. In some embodiments, when the discoverypacket 300 is configured without a header, a DMRS may be selected toindicate the payload size and/or the modulation and coding scheme (MCS)of the discovery payload 304. In some embodiments, when the discoverypacket 320 is configured with a header 322, the discovery header 322 mayindicate the payload size and/or MCS of the discovery payload 324. Insome embodiments, when the discovery packet 300 is configured without aheader, payload size and MCS of the discovery payload 304 may bepredetermined. These embodiments, as well as other embodiments, arediscussed in more detail below.

Referring to FIG. 3A, a UE 112 may configure and transmit the discoverypacket 300 in accordance with the predetermined configuration (FIG. 3A)without a header. In some of these embodiments, the UE 112 may transmitan uplink DMRS. The DMRS may be selected to indicate the payload sizeand/or MCS of the discovery payload. In these embodiments, the payloadsize and MCS may be mapped to a particular DMRS. In these embodiments,the base sequence, the cyclic shift value and/or the orthogonal covercode of the DMRS may indicate one or more of the payload size and MCS ofthe discovery packet 300. In some of these embodiments, the basesequence, the cyclic shift value and/or the orthogonal cover code of theDMRS may indicate one or more payload size and MCS combinations.

In some embodiments, when the discovery packet 300 is configured andtransmitted without a header, the discovery payload 304 may configurableto have one of a plurality of predetermined payload size and MCScombinations. Each of the predetermined payload size and MCScombinations may be mapped to one of a plurality of base sequences ofthe DMRS. The UE 112 may select a DMRS having one of the base sequencesbased on the payload size and MCS combination of the discovery packet300. In some of these embodiments, the transmitting UE 112 may select abase sequence for the DMRS from a plurality of base sequences based onthe payload size, the MCS or a combination of the payload size and theMCS of the discovery packet 300. The receiving UE 114 may perform ablind detection technique on the DMRS to search the plurality of basesequences to identify the particular base sequence to determined payloadsize and/or MCS of the discovery packet. In some of these embodiments,the MCS may be predetermined (i.e., fixed) and therefore only thepayload size would be mapped to a particular one of the base sequencesof the DMRS.

In some embodiments, when the discovery packet 300 is configured andtransmitted without a header, the discovery payload 304 may beconfigurable to have one of a plurality of predetermined payload sizeand MCS combinations. Each of the predetermined payload size and MCScombinations may be mapped to one of a plurality of cyclic shifts (CS)values and/or an orthogonal cover codes (OCCs) of the DMRS. The UE 112may select a DMRS (e.g., from a subset of DMRSs) to have a CS value andOCC based on the payload size and MCS combination of the discoverypacket 300. In these embodiments, the receiving UE 114 may be able todetermine the payload size and the MCS of the discovery packet 300 fromthe CS value and the OCC of the DMRS. In some of these embodiments, thebase sequence of the DMRS would not provide any indication of thepayload size and the MCS of the discovery packet, although the scope ofthe embodiments is not limited in this respect as the base sequence mayalso be used to indicate the payload size and/or the MCS. In theseembodiments, the UE may select one DMRS from a subset of possible DMRSsfor discovery packet transmission (e.g., with n_(CS)ε{0,4,8} andn_(oc)ε{0,1}, where n_(CS) is the cyclic shift index and n_(oc) is theorthogonal cover code index). In these embodiments, for example, onesubset of DMRS sequences with n_(CS)ε{0,4,8} and n_(oc)ε{0} may be usedto indicate a discovery payload size of X bits while another subset ofDMRS sequences with n_(CS)ε{0,4,8} and n_(oc)ε{1} may be used toindicate a discovery payload size of Y bits. Although these embodimentsdo not increase the number of blind detections for the case that thetransmitting UE 112 randomly chooses a cyclic shift, these embodimentsmay effectively reduce the minimum distance between cyclic shifts if alltransmitting UEs within radio range select the same payload size and MCSconfiguration.

In some embodiments, when the discovery packet 300 is configured andtransmitted without a header, the discovery payload 304 may beconfigured to have a predetermined payload size, and to have apredetermined modulation and coding scheme (MCS). In some exampleembodiments, a predetermined payload size may be 192 bits, although thescope of the embodiments is not limited in this respect. In some exampleembodiments, a predetermined MCS the discovery payload 304 may be QPSK,although the scope of the embodiments is not limited in this respect.The use of a predetermined payload size and predetermined MCS allows thereceiving UE 114 to receive and decode the discovery packet withoutadditional processing (e.g., blind detection) to determine the payloadsize and MCS. In these embodiments, the receiving UE 114 may beconfigured to receive discovery packets 300 of a predeterminedconfiguration within resources that are indicated for D2D discovery.

Referring to FIG. 3B, in some embodiments the UE 112 is arranged toconfigure and transmit the discovery packet 320 in accordance with thepredetermined configuration (FIG. 3B) with a discovery header 322. Inthese embodiments, the discovery header 322 may be configured toindicate one of a plurality of predetermined payload size and MCScombinations of the discovery payload 324. In these embodiments thatinclude a discovery header 322, the discovery packet 320 may beconsidered a discovery frame. In these embodiments, the discovery header322 may be limited to a predetermined number of bits (e.g., two bits) toindicate one of several predetermined payload size and MCS combinations.In some of these embodiments, the MCS of the discovery payload 324 maybe predetermined (i.e., fixed) in which the discovery header 322 mayonly indicate the payload size.

In some of these embodiments in which the UE 112 is arranged toconfigure and transmit the discovery packet 320 with a discovery header322, the discovery header 322 may be configured with a lower coding ratethan the discovery payload 324. The discovery header 322 may have apredetermined (i.e., a deterministic) MCS. In these embodiments, thecoding rate and modulation (i.e., the MCS) of the discovery header 322may be predetermined and may be known to the receiving UE 114 allowingthe receiving UE 114 to easily and quickly decode the discovery header322. The use of a lower coding rate for the discovery header 322 mayhelp to ensure more robust reception of the discovery header 322. Inthese embodiments, a repetition code or a lower coding rate of ½ may beused for the discovery header 322 while a greater coding rate of ⅔, ¾, ⅚or ⅞ may be used for the discovery payload 324 depending on the level ofrobustness desired. In these embodiments, QPSK modulation, for example,may be used for both the discovery header 322 and the discovery payload324, although the scope of the embodiments is not limited in thisrespect.

In some embodiments, the coding rate of the discovery payload 304/324(FIG. 3A/3B) may correspond to different levels of robustness. The UE112 may select the coding for the discovery payload 304/324 based on adesired level of robustness. In these embodiments, the discovery packetmay be configured without a header or with a header. In someembodiments, prior to configuring the discovery packet 300/320, the UE112 may perform a proximity sensing process to identify the receiving UE114 (as well as other ProSe enabled devices in its proximity). The UE112 may select one of the levels of robustness based on a range (orproximity) to the receiving UE 114 and/or channel conditions. In theseembodiments, lower coding rates (more coding bits) and smaller payloadsize combinations may be used from a longer range (greater robustnessmay be needed), while higher coding rates and larger payload sizecombinations may be used for a shorter range (less robustness may beneeded). In these embodiments, the range to the receiving UE 114 may bebased on received signal power from the receiving UE 114, although thisis not a requirement as other range estimation and proximity detectiontechniques may be used. These embodiments may be employed with orwithout transmit power control (TPC).

In some of these embodiments in which the UE 112 is arranged toconfigure and transmit the discovery packet 320 with a discovery header322, the discovery header 322 may be mapped to one or more REs 211 (FIG.2) that are allocated for D2D discovery and that are adjacent to anuplink PUSCH DMRS symbol (e.g., DMRS symbol 210 (FIG. 2)) in order totake advantage of the best possible channel estimation since the DMRSmay be used by UEs for channel estimation. In these embodiments, thediscovery payload 324 may be mapped to REs allocated for D2D discoveryother than REs used for the discovery header and REs used for the uplinkPUSCH DMRS symbol. In these embodiments, the discovery header 322 may betransmitted in REs 211 adjacent to the DMRS symbol 210 while some of theremaining REs (i.e., REs of discovery zone 204 except REs used fordiscovery header and DMRS symbol) may be used for transmission of thediscovery payload 324.

For example, if one resource block has one PRB pair (e.g., 14 OFDMsymbols in the time domain and one PRB in the frequency domain), theDM-RS symbols may be located in 4th and 11^(th) OFDM symbols. Thediscovery header 322 may be mapped to some REs in the 3^(rd) and 12thOFDM symbols while the remaining REs may be used for discovery payloadmapping. In these embodiments, the discovery header 322 and thediscovery payload are multiplexed in the same discovery resource 324.

In some embodiments, the UE 112 may transmit the discovery packet300/320 in accordance with a single-carrier frequency division multipleaccess (SC-FDMA) technique on discovery resources of a discovery zone204, although this is not a requirements. In other alternateembodiments, the UE 112 may transmit the discovery packet 300/320 inaccordance with an OFDMA technique.

In some embodiments, the UE 112 may append the discovery packet 300/320with parity check bits when turbo coding is employed for channel coding.In these embodiments, turbo coding, such as the turbo coding techniquespecified in 3GPP TS36.212, may be reused for D2D discovery, althoughthe scope of the embodiments is not limited in this respect.

In some embodiments, after adding the CRC 306/326 to a discovery packet300/320, the UE 112 may encode the discovery packet 300/320 inaccordance with a tail-biting convolutional coding (TBCC) technique whenTBCC is used (i.e., instead of turbo coding). In these embodiments thatemploy TBCC, the discovery packet 300/320 may be appended withadditional parity check bits. In these embodiments, the TBCC techniquespecified in 3GPP TS36.212 may be reused for D2D discovery, although thescope of the embodiments is not limited in this respect.

In some embodiments, after channel coding, the UE 112 may perform ratematching based on an amount of resources to be used for the D2Dtransmission of the discovery packet 300/320. During rate matching,coded bits (after channel coding) may be rate-matched to fill the amountof resources (e.g., PRBs) to be used for the D2D transmission of thediscovery packet 300/320. In these embodiments, the rate matching andinterleaver as specified in 3GPP TS36.212 may be reused for D2Ddiscovery, although the scope of the embodiments is not limited in thisrespect. In accordance with some of these embodiments, one or more PRBpairs may be used for transmission of the discovery packet 300/320depending on the payload size and performance requirements. In theseembodiments, the rate matching may include generating a number of bitsbased on the number of PRBs allocated for transmission from a fixed-ratemother code. This may be realized by repeating or puncturing the bits ofa mother codeword.

In some embodiments, after the rate matching, the UE 112 may perform bitscrambling on the coded bits in accordance with a scrambling sequence. Ascrambling identity may be used to initialize the scrambling sequence.The scrambling identity may either be a cell identity (ID), a commonscrambling identity, a function of the discovery resources used fortransmission of the discovery packet 300/320, a function of the cyclicshift value and/or OCC index of the DMRS that is transmitted by the UE112 or a common D2D scrambling identity or a combination of the theseparameters. In these embodiments, the use of bit scrambling may helprandomize interference and improve the ability of the receiving UE 114to receive and decode the discovery packet 300/320.

In some embodiments, the signaling received from the eNB 104 mayindicate that the discovery zone 204 is either semi-statically signaledusing radio-resource control (RRC) signaling or may be provided in oneor more system-information blocks (SIBs). The UE 112 may be configurableby the eNB 104 for either Type 1 D2D discovery or Type 2 D2D discovery.When configured for Type 1 D2D discovery, resources for transmission ofthe discovery packet 300/320 are allocated by the eNB 104 on a non-UEspecific basis. When configured for Type 2 D2D discovery, specificresources for transmission of the discovery packet 300/320 are allocatedby the eNB 104 to the UE 112. In some embodiments, for type 1 discovery(contention based D2D discovery or D2D discovery with UE-autonomousselection of discovery resources), a ProSe enabled device may randomlyselect the DMRS sequence when transmitting the discovery packet (e.g.,when a discovery header is used or when the discovery payload size andMCS are predetermined).

In some embodiments, the discovery-related content included in thediscovery payload 304/324 (FIG. 3A/3B) may include a unique ID fordevice identification, a service identifier, etc. In some embodiments,the size of the discovery payload may range from 48 bits or less to upto 100 bits or more. In some embodiments, for non-public safety service,the discovery payload 304/324 may include a ProSe application code, aProSe function ID and a public land mobile network (PLMN) ID. For publicsafety service, the discovery payload 304/324 may includesource/destination ID, a message type, a ProSe application ID, etc. Insome embodiments, the destination ID may identify a single UE or a groupof UEs that are the intended recipients of the discovery packet. In someembodiments, a UE mode of operation may be indicated which may definewhether a public safety ProSe UE is acting as a UE-to-network relay, aUE-to-UE relay or both, or not acting as a relay.

FIG. 4 illustrates D2D discovery packet processing 400 in accordancewith some embodiments. The elements illustrated in FIG. 4 may beperformed by a physical layer, such as the physical layer (PHY)circuitry of a UE, such as UE 112 (FIG. 1).

The physical layer processing 400 may include attaching a CRC to thediscovery packet at CRC attachment 402. The CRC attachment may be eitherprocessed in the physical layer or in the MAC layer. The CRC attachmentmay be optional. In addition, 8, 16 or 24 parity check bits may be usedfor packet-based D2D discovery design.

The physical layer processing 400 may include channel coding 404.Different from the Turbo coding scheme adopted for PUSCH, tail-bitingconvolutional coding (TBCC) used in PDCCH may be performed forpacket-based D2D discovery and may provide improved performance andreduced decoding complexity. Furthermore, TBCC coding scheme mayoutperform Turbo coding for a packet with relatively small payload size,such as a discovery packet. For example, TBCC may achieve better linklevel discovery performance than Turbo coding when the payload size is48 bits. When the payload size is 176 bits, Turbo coding may slightlyoutperform the TBCC, depending on various factors. Additionally, QPSKmay provide considerable performance gain compared to 16QAM for bothpayload sizes.

The physical layer processing 400 may include rate matching 406. Afterthe channel coding, coded bits may be rate-matched to fill into theamount of resources available for the D2D discovery transmission. Thatthe amount of resource blocks for packet-based D2D discovery may be oneor more PRB pairs, depending on the payload size and overall discoveryperformance requirement. In addition, the PRB size may be limited to theproducts of the integers 2, 3, and 5 as specified for PUSCH transmissionof SC-OFDM waveform to reduce the implementation cost, although thescope of the embodiments is not limited in this respect.

The physical layer processing 400 may include scrambling 408. In orderto help randomize the interference, bit scrambling may be applied afterrate-matching. The scrambling identity for the initialization ofscrambling sequence may be available at the discovering UE 112 to ensureproper and efficient decoding process. For both open and restricteddiscovery, a common scrambling identity may be used for all ProSeenabled devices within the network 100. This scrambling identity may beconfigured as a common D2D scrambling identity, although the scope ofthe embodiments is not limited in this respect. For example, forintra-cell discovery, this scrambling identity may be configured as thecell ID. For inter-cell or inter-PLMN discovery, the scrambling identitymay be configured as a virtual scrambling identity, which may bepredefined or broadcast by an eNB 104.

When the scrambling identity is configured as cell ID, the scramblingsequence generator may be initialized with:

c _(init) =f(N _(ID) ^(cell))

where N_(ID) ^(cell) is the cell ID. One straightforward way is todefine the scrambling identity as c_(init)=N_(ID) ^(cell).

As mentioned above, the scrambling identity may be configured as commonscrambling identity,

c _(init) =f(N _(ID) ^(D2D))

where N_(ID) ^(D2D) is the virtual scrambling identity. One way is todefine the scrambling identity as c_(init)=N_(ID) ^(D2D).

In some alternate embodiments, the scrambling identity may be configuredas a function of discovery resource index (i.e., time and frequencyindex within the discovery zone), the cyclic shift index used for DMRSsequence transmission or cell ID, a common D2D scrambling identity orany combination of the above parameters. In some embodiments, thescrambling identity may be defined as a function of the cyclic shiftindex and/or OCC index used for DMRS sequence transmission and cell IDor common scrambling identity as follows:

c _(init) =f(n _(CS) ,N _(ID) ^(cell))

where n_(CS) is the DMRS sequence index, which may be a function ofcyclic shift index and/or OCC index. For open discovery, a UE 102 mayrandomly select the cyclic shift index for DMRS sequence transmission.One approach is to define the scrambling identity as

c _(init) =n _(CS) ·c ₀ +N _(ID) ^(cell).

where c₀ is a constant. For instance, c₀ may be chosen as 2¹⁴ to savethe computational complexity.

In some alternate embodiments, the scrambling identity may be defined asa function of discovery resource index, cyclic shift index used for DMRSsequence transmission and cell ID or common scrambling identity:

c _(init) =f(n _(s) ,n _(f) ,n _(CS) ,N _(ID) ^(cell)),

where n_(s) is the subframe index within the discovery zone and n_(f) isthe PRB index within the discovery zone. One approach is to define thescrambling identity as:

c _(init) =n _(s) ·c ₀ +n _(f) ·c ₁ +n _(CS) ·c ₂ +N _(ID) ^(cell).

where c₀, c₁ and c₂ are the constants. In some embodiments, c₀, c₁ andc₂ may be chosen as a power of two to save the computational complexity.

The physical layer processing 400 may include modulation 410. Themodulation schemes supported for PUSCH transmission may include QPSK,16QAM and 64QAM. For the discovery payload 304/324, different modulationschemes may be used, however, QPSK modulation scheme may be desirablefor the discovery header 322, although the scope of the embodiments isnot limited in this respect.

The physical layer processing 400 may include discrete Fourier transform(DFT) precoding 412. Similar to a PUSCH transmission, DFT precoding maybe utilized for packet-based D2D discovery in order to reduce thepeak-to-average power ratio (PAPR), which can improve the transmit powerefficiency and may potentially increase the discovery range forProSe-enabled devices.

The physical layer processing 400 may include resource mapping 414. Thediscovery resources for packet transmission may be either randomlyselected from within the configured discovery zone 204 by a ProSe enabledevice in contention-based discovery or explicitly allocated by an eNB104 in non-contention-based discovery. In some embodiments, amulti-cluster PUSCH transmission may be applied for packet-based D2Ddiscovery to exploit the benefits of frequency diversity. The frequencygap between two clusters may be configured and addressed appropriatelyin order to reduce the co-channel interference in the discovery region.

The physical layer processing 400 may include antenna mapping 416. Whena ProSe-enabled device is equipped with multiple transmit antennas, amulti-antenna transmission scheme may be employed to further improve thelink level performance. A common precoder structure may be used for openD2D discovery to allow power-efficient discovery.

The physical layer processing 400 may include SC-FDMA symbol generation418. SC-FDMA symbol generation procedure for PUSCH transmission may bebe reused for packet-based D2D discovery design, including cyclic-prefix(CP) insertion and a half-subcarrier shift.

As discussed above, the uplink PUSCH DMRS may primarily be used forchannel estimation for coherent demodulation of the PUSCH. Forpacket-based D2D discovery, a similar DMRS sequence generation procedurebased on Zadoff-Chu sequences may be adopted. A UE specific cyclic shiftmay be either randomly selected by ProSe-enabled devices in contentionbased discovery scenario or explicitly signaled by an eNB 104 incontention free discovery scenario. With respect to the DMRS basesequences, a common base sequence may be used by all ProSe-enableddevices, which may reduce the amount of blind detections at thediscovery UEs significantly. Alternatively, the base sequence may beselected or chosen as a function of the cell on which an RRC_IDLE D2Ddevice camps on or an RRC_CONNECTED D2D device is associated to (forwithin network coverage scenarios) and a function of the identity of thePeer Radio Head (PRH) or cluster head (for partial or outside networkcoverage scenarios). This may help improve the robustness of the channelestimation via interference averaging effects. Note that whilesequence-group hopping may be disabled for discovery packettransmissions, cyclic shift hopping may be enabled if the base sequencenot common and is a function of camping cell-ID, PRH-ID, etc. asdescribed above. In some embodiments, ProSe-enabled UEs may randomlychoose one of two OCCs for the PUSCH DMRS, although the scope of theembodiments is not limited in this respect.

In order to exploit the benefits of frequency diversity, frequencyhopping may be adopted for packet-based D2D discovery. Similar tofrequency hopping for PUSCH transmission, two options of hopping patterndesign may be employed: type-1 D2D discovery hopping utilizes theexplicit hopping pattern; while type 2 D2D discovery hopping uses thesubband hopping and mirroring mechanism. In addition, the hoppingprocedure may follow either intra-subframe or inter-subframe basedhopping mode. Selection between type-1 and type-2 discovery hopping, aswell as intra-subframe and inter-subframe hopping may be provided byhigher layer in a cell-specific manner.

FIG. 5 illustrates a functional block diagram of a UE in accordance withsome embodiments. The UE 500 may be suitable for use as any one or moreof the UEs 102 illustrated in FIG. 1, including UE 112 and UE 114. TheUE 500 may include physical layer (PHY) circuitry 502 for transmittingand receiving signals to and from eNBs 104 (FIG. 1) using one or moreantennas 501 as well as for D2D communications with other UEs. UE 500may also include medium access control layer (MAC) circuitry 504 forcontrolling access to the wireless medium. UE 500 may also includeprocessing circuitry 506 and memory 508 arranged to configure thevarious elements of the UE 500 to perform the various operationsdescribed herein.

In accordance with some embodiments, the UE 500, while in either RRCidle or RRC connected mode, may be configured to transmit a discoverypacket 101 (FIG. 1) to discover another UE as described herein andreceive responses to the discovery packet 101 from the other UE. The UE500 may also be configured to monitor and attempt to decode a receiveddiscovery packet that is transmitted in the discovery zone 204 (FIG. 2)by another UE for discovery by the other UE. The UE 500 may also bearranged to establish a D2D connection with another UE after eitherdiscovering the other UE or after being discovered by another UE. Thechannel resources for the D2D discovery and the D2D connection may beassigned by the eNB 104 as discussed herein.

In accordance with some embodiments, the UE 500 may be configured toreceive signaling from an eNB 104 indicating resources of the discoveryzone 204 allocated for D2D discovery and may configure a discoverypacket 300/320 in accordance with a predetermined configuration to haveat least a discovery payload 304/324 and a CRC 306/326. The discoverypayload may be configured include discovery-related content. The UE 500may also transmit the discovery packet 300/320 on at least some of theindicated discovery resources for receipt by a receiving UE.

In some embodiments, the UE 500 may a portable wireless communicationdevice or a mobile device, such as a personal digital assistant (PDA), alaptop or portable computer with wireless communication capability, aweb tablet, a wireless telephone, a smartphone, a wireless headset, apager, an instant messaging device, a digital camera, an access point, atelevision, a medical device (e.g., a heart rate monitor, a bloodpressure monitor, etc.), or other device that may receive and/ortransmit information wirelessly. In some embodiments, the mobile devicemay include one or more of a keyboard, a display, a non-volatile memoryport, multiple antennas, a graphics processor, an application processor,speakers, and other mobile device elements. The display may be an LCDscreen including a touch screen.

The antennas 501 may comprise one or more directional or omnidirectionalantennas, including, for example, dipole antennas, monopole antennas,patch antennas, loop antennas, microstrip antennas or other types ofantennas suitable for transmission of RF signals. In some multiple-inputmultiple-output (MIMO) embodiments, the antennas may be effectivelyseparated to take advantage of spatial diversity and the differentchannel characteristics that may result.

Although the UE 500 is illustrated as having several separate functionalelements, one or more of the functional elements may be combined and maybe implemented by combinations of software-configured elements, such asprocessing elements including digital signal processors (DSPs), and/orother hardware elements. For example, some elements may comprise one ormore microprocessors, DSPs, field-programmable gate arrays (FPGAs),application specific integrated circuits (ASICs), radio-frequencyintegrated circuits (RFICs) and combinations of various hardware andlogic circuitry for performing at least the functions described herein.In some embodiments, the functional elements may refer to one or moreprocesses operating on one or more processing elements.

Embodiments may be implemented in one or a combination of hardware,firmware and software. Embodiments may also be implemented asinstructions stored on a computer-readable storage device, which may beread and executed by at least one processor to perform the operationsdescribed herein. A computer-readable storage device may include anynon-transitory mechanism for storing information in a form readable by amachine (e.g., a computer). For example, a computer-readable storagedevice may include read-only memory (ROM), random-access memory (RAM),magnetic disk storage media, optical storage media, flash-memorydevices, and other storage devices and media. Some embodiments mayinclude one or more processors and may be configured with instructionsstored on a computer-readable storage device.

FIG. 6 is a procedure for packet-based D2D discovery in accordance withsome embodiments. Discovery procedure 600 may be performed by a ProSeenabled UE arranged for packet-based D2D discovery, such as UE 112 (FIG.1).

Operation 602 may include receiving signaling from an eNB 104 indicatingresources allocated for D2D discovery.

Operation 604 may include configuring a discovery packet 300/320 inaccordance with a predetermined configuration to have at least adiscovery payload 304/324 and a CRC. The discovery payload may includediscovery-related content.

Operation 606 may include transmitting the configured discovery packet300/320 on at least some of the indicated discovery resources (e.g.,PRBs 206 of discovery zone 204) for receipt by a receiving, such as UE114 (FIG. 1).

The Abstract is provided to comply with 37 C.F.R. Section 1.72(b)requiring an abstract that will allow the reader to ascertain the natureand gist of the technical disclosure. It is submitted with theunderstanding that it will not be used to limit or interpret the scopeor meaning of the claims. The following claims are hereby incorporatedinto the detailed description, with each claim standing on its own as aseparate embodiment.

What is claimed is:
 1. An apparatus of a user equipment (UE) configuredfor proximity communications (ProSe), the apparatus comprising: memory;and processing circuitry, configured to: decode a system informationblock (SIB) from an enhanced node B (eNB), the SIB comprising discoveryresource configuration information for direct UE-to-UE communications,the SIB including an indication of resources of a discovery resourcepool for transmission and/or reception of discovery packets; encode adiscovery packet to include a discovery payload and a cyclic-redundancycheck (CRC); perform bit scrambling on coded bits of the discoverypacket in accordance with a scrambling sequence; configure the encodeddiscovery packet for transmission within the resources of the discoveryresource pool; and generate a demodulation reference signal (DMRS) fortransmission within the resources of the discovery resource pool, theDMRS mapped to a base sequence configured for demodulation of thediscovery packet by another UE.
 2. The apparatus of claim 1 wherein theprocessing circuitry is further configured to initialize the scramblingsequence with a scrambling identity at a start of each of a plurality ofsubframes.
 3. The apparatus of claim 2, wherein the apparatus furthercomprises a sequence generator, and wherein for discovery packettransmissions, the sequence generator is initialized with the scramblingidentity at the start of each subframe of the plurality.
 4. Theapparatus of claim 1, wherein the SIB indicates whether the resources ofthe discovery resource pool are commonly allocated for device-to-devicecommunication, or individually allocated for direct UE-to-UEcommunication.
 5. The apparatus of claim 1 wherein the discovery packetis configured to be transmitted without a header.
 6. The apparatus ofclaim 1 wherein the resources of the discovery resource pool arescheduled periodically.
 7. The apparatus of claim 1 wherein thediscovery packet is configured to have a predetermined size; and whereinthe discovery packet is encoded for transmission in accordance with aquadrature phase-shift keying (QPSK) modulation scheme
 8. The apparatusof claim 1 further comprising transceiver circuitry coupled to one ormore antennas, the transceiver circuitry configured to: receive the SIBfrom the eNB; transmit the encoded discovery packet within the resourcesof the discovery resource pool in accordance with a modulation scheme;and transmit the DMRS within the resources of the discovery resourcepool.
 9. The apparatus of claim 8 wherein the transceiver circuitry isfurther configured to transmit the encoded discovery packet inaccordance with a single-carrier frequency-division multiple access(SC-FDMA) technique within resources of the discovery resource pool, andwherein the processing circuitry is configured to monitor some of theresources of the discovery resource pool for discovery announcementsfrom other UEs.
 10. The apparatus of claim 9 wherein the processingcircuitry comprises a baseband processor.
 11. A non-transitorycomputer-readable storage medium that stores instructions for executionby processing circuitry of a user equipment (UE) to configure the UE forproximity communications (ProSe), the processing circuitry, configuredto: decode a system information block (SIB) from an enhanced node B(eNB), the SIB comprising discovery resource configuration informationfor direct UE-to-UE communications, the SIB including an indication ofresources of a discovery resource pool for transmission and/or receptionof discovery packets; encode a discovery packet to include a discoverypayload and a cyclic-redundancy check (CRC); perform bit scrambling oncoded bits of the discovery packet in accordance with a scramblingsequence; configure the encoded discovery packet for transmission withinthe resources of the discovery resource pool; and generate ademodulation reference signal (DMRS) for transmission within theresources of the discovery resource pool, the DMRS mapped to a basesequence configured for demodulation of the discovery packet by anotherUE.
 12. The non-transitory computer-readable storage medium of claim 11wherein the processing circuitry is further configured to initialize thescrambling sequence with a scrambling identity at a start of each of aplurality of subframes.
 13. The non-transitory computer-readable storagemedium of claim 11, wherein the SIB indicates whether the resources ofthe discovery resource pool are commonly allocated for device-to-devicecommunication, or individually allocated for direct UE-to-UEcommunication.
 14. The non-transitory computer-readable storage mediumof claim 11 wherein the resources of the discovery resource pool arescheduled periodically.
 15. An apparatus of a user equipment (UE)configured for proximity communications (ProSe), the apparatuscomprising: memory; and processing circuitry, configured to: decode asystem information block (SIB) from an enhanced node B (eNB), the SIBcomprising discovery resource configuration information for directUE-to-UE communications, the SIB including an indication of resources ofa discovery resource pool for transmission and/or reception of discoverypackets; monitor some of the resources of the discovery resource poolfor discovery announcements from other UEs; decode an encoded discoverypacket received within the resources of the discovery resource pool, theencoded discovery packet modulated in accordance with a predeterminedmodulation scheme, the discovery packet including a discovery payloadand a cyclic-redundancy check (CRC); and decode a demodulation referencesignal (DMRS) received within the resources of the discovery resourcepool, the DMRS mapped to a base sequence configured for demodulation ofthe discovery packet by the UE.
 16. The apparatus of claim 15, whereinthe SIB indicates whether the resources of the discovery resource poolare commonly allocated for device-to-device communication, orindividually allocated for UE-to-UE communication.
 17. The apparatus ofclaim 15 wherein the resources of the discovery resource pool arescheduled periodically.
 18. The apparatus of claim 15 further comprisingtransceiver circuitry coupled to one or more antennas, the transceivercircuitry configured to: receive the SIB from the eNB; receive theencoded discovery packet within the resources of the discovery resourcepool in accordance with the predetermined modulation scheme; and receivethe DMRS within the resources of the discovery resource pool.